The present invention refers to a method of and apparatus for pneumatically conveying bulk material in form of granular solids or the like though a transport pipe.
In general, the material to be conveyed is mixed with carrier gas, in particular compressed air and sent under pressure from a feeder such as a rotary feeder, lock or the like in the transport pipe. Recently, there is a trend to conduct the transport at very low velocities of the material and at increased charge of the carrier gas. A transport of bulk material under such conditions has the advantage that the material and the conveyor are protected against wear and destruction and allows the use of small quantities of carrier gas. This in turn facilitates dedusting and saves energy.
A further decrease of the conveying velocity at increased charge of the carrier gas is, however, only possible up to a certain point because of the increasing pressure drag caused by the friction of the carrier gas and material to be conveyed on the inner pipe wall surface and the resulting clogging and formation of blockages in the transport pipe. In order to remove such clogging or blockages, methods were proposed by which auxiliary air or bypass air was fed into the transport pipe. This, however, rendered the conveyor complicated and inefficient.
German patent DE-PS 32 12 782 discloses a method of pneumatically conveying granular material with a transport pipe which is completely filled with material and which is subjected to vibrations and simultaneously set under pressure. The vibrations are applied in axial direction or in circumferential direction relative to the pipe and result in a frictional reduction between the material and the pipe wall. Although a desired slow transport of the combined carrier gas/material column is attained, the conveying capacity is still too limited as only conveying velocities of up to 20 cm/s can be reached. An increase of the conveying capacity is not feasible as the conveying velocity would become too low. Moreover, the conveyor becomes relative complicated when desiring to deflect the transport pipe in a different direction.